Ok im confused with the different answers
I understand what wheresmycar is trying to say, but he comes off as a bit wrong. (and to suggest the 1050 instead of the 1050TI is just weird considering they are so close in performance.) Basically he's trying to say that the APUs from AMD aren't worth using a dGPU. In a word I would say wrong. AMDs CPU issue has been going on for awhile and most of the time their CPUs are enough, but there are enough "random" times they aren't that I don't really suggest using them. You are already using one of the best APUs so I'm going to give you the same advice I give to people using the 8320, etc. First, some proof that the 7890K isn't horrid.
http://www.anandtech.com/show/9307/the-kaveri-refresh-godavari-review-testing-amds-a10-7870k/6
Here they are testing the 7870K and other CPUs with either an R9285 or the GTX770. Notice that in Alien: Isolation the 7870 sits at the top of the APUs, and JUST behind the Intel CPUs when testing with both GPUs. In fact unless you go down to the lowest A8 or A6 APUs they all perform around the same. When looking at GTA:V it's still able to stay in the mix. To claim that you shouldn't put a GPU into a system with an APU is a very odd thing to claim.
That said the APU isn't the best gaming processing unit to have. If you look at the results for GRID, none of the APUs are able to hit 60FPS while all of the Intel CPUs can with the 285. I would argue it's safe to add the best GPU you can with the understanding that some games here and there will fall short. To fix this you need to stop using AMDs older CPUs and use either Intel CPUs or the new Ryzen CPUs from AMD. Either option will require a new motherboard and ram however so it's not cheap.